Recent studies have examined: 1) the renal effects of enflurane and halothane anesthesia in rats with abnormal renal function additionally administered gentamicin, 5mg/kg/day. No significant change in renal function could be attributed to either anesthetic agent. Serum inorganic fluoride levels four hours (22-25 uM) and 24 hours (5uM) after enflurane anesthesia were similar in the gentamicin treated and the non-gentamicin treated groups; 2) the effects of isoniazid treatment on metabolims of fluorinated ether anesthetics in vivo and in vitro. Previous studies have shown that enzyme induction with phenobarbital did not enhance enflurane defluorination. In this study, 50 mg/kg/day of isoniazid increased defluorination of enflurane 370%, methoxyflurane 259%, sevoflurane 283%, and isoflurane 168%. Enhanced microsomal defluorination was not associated with an increase in total cytochrome P-450 content. In vivo, Fischer 344 rats treated with INH became markedly polyuric 24 hours after enflurane anesthesia as compared to saline treated animals. Additionally, serum fluoride and BUN levels were significantly elevated in INH treated animals compared to those administered saline and enflurane; 3) anesthetic defluorination and liver function were examined in Fischer 344 rats with chronic, terminal failure. In vivo liver function was normal, as was in vitro defluorination of the fluorinated anesthetics. Cytochrome P-450 levels were not decreased. Thus, normal serum fluoride levels after enflurane anesthesia seen in rats with impaired renal function must be due to enhanced extrarenal fluoride clearance, probably into bone.